1. Field
The present disclosure relates to aircraft external power supply protection systems, more specifically to external power indicators and starter power supply circuits.
2. Description of Related Art
Aircraft can draw power from an external source when on the ground to power electronic systems and to avoid draining the battery when using high draw systems like the starter for an auxiliary power unit (APU). Such aircraft have an external power receptacle on the airframe for maintenance personal to plug an external DC power cart into the plane. Indicators such as “Available” and “In Use” can be disposed next to the receptacle and/or in the cockpit to indicate that external power is either available and/or in use, respectively. Also, a manual switch (usually push-button, push on, push off type) to change from aircraft battery power to external DC power can be included near the receptacle on the outside of the plane and/or in the cockpit.
Traditional indicators may operate even when insufficient power is supplied by the external DC power cart. For example, the “Available” indicator may activate at a lower voltage than required by the internal power switching circuitry causing a false indication of acceptable power supply. In such an instance, if the switch is thrown to change from battery to external DC power and the DC power voltage is too low to activate the electrical power distribution circuit (EPDC), the “Available” indicator will stay activated and nothing will happen (e.g., the “In Use” indicator would not activate), potentially causing confusion.
In a typical situation where the external DC power voltage is too high, the “Available” indicator will illuminate and potentially burn out. When the switch is pressed, the “In Use” indicator would briefly activate, and then both indicators would shut down due to over-voltage protection in the aircraft circuitry. After the manual switch is opened (pressed again) to activate the battery supply, the “Available” light would illuminate again (if it did not burn out) causing potential confusion and a likely over-voltage repeat by the user. Consequently, operators of such systems must learn to understand the indicator light behavior and use other information in situations such as those described above.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved external power supply monitoring, indicating, and switching systems. The present disclosure provides a solution for this need.